BCL2 and B-cell chronic lymphocytic leukemia: BCL2 variants that have been observed to emerge in patients with CLL progressing on venetoclax in several independent clinical cohorts include Gly101Val [61], Asp103Tyr/Glu [62, 66, 67] and Phe104Leu/Ile/Cys [68], with experimental evidence supporting decreased drug binding but retention of pro-survival function.